1. Field of the Invention
The present invention relates to a method for recognizing an obstructed situation of a motor-driven traveling element by evaluating a variable containing information about the rotational speed of the motor.
2. Background Art
Methods are used to detect obstructive situations of a motor-driven element such as an electric motor-driven element. Such obstructive situations occur, for example, when something is being pinched. Such methods are used, for example, to operate a window raising motor which closes a window in a motor vehicle. The methods are intended to ensure that objects, especially parts of a person's body, are not pinched in the closing window gap when the window is closed. The information about the rotational speed of the motor that is used for detecting obstructive situations is the motor period. The motor period is typically supplied by arranging a magnet having multiple poles in the peripheral direction on the armature shaft of the drive motor. The respective polarity is detected with a stationary Hall sensor or stationary Hall sensor arrangement.
It is possible to determine the rotational speed of the motor from the length of time a polarity is detected. This is because the length of time a polarity is detected is an analog signal representing the traversal of the motor through a certain rotational angle. If something is being pinched, the duration of the motor periods increase because the motor speed is reduced by the obstacle. To detect such an obstructed situation or such a case of pinching, the length of each detected motor period is compared with a predefined threshold value.
The magnitude of the threshold is chosen such that the threshold is not exceeded when the window makes a closing motion under normal conditions. This threshold, which is also called a cut-off value, being exceeded is indicative of pinching. To verify with greater probability that there actually is pinching when the cut-off value is exceeded, the durations (i.e., lengths) of a few more motor periods are evaluated. If the durations of these motor periods also exceed the cut-off value, it is concluded that there is pinching and the motor is reversed to lower the window.
Even if this method is fundamentally satisfactory at detecting cases of pinching when motor-driven windows in motor vehicles are closed, the system also concludes that a pinching situation is present in other cases whenever the above-mentioned conditions are met. These conditions are also met when the window is exposed to shocks when it is being closed such as which occur when driving through potholes on a rough road. Such erroneous reversals can be reduced by setting the cut-off value relatively high. However, if the recognition method has its cut-off value set too high, then it recognizes a case of pinching at a relatively late point in time.